This is a version of Bollinger bands made as a filled area. But
to avoid just making the usual Bollinger bands with some more colors,
this version has a choice of calculating the standard deviation as a
sample or as an uncorrected deviation. The explanation for that would be
the following.

The difference is usually not big, but it exists. So now we have the
Bollinger bands with a choice of these two deviation types too (with the
usual set of 22 price types addition).